1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the semiconductor device.
It is to be noted that the semiconductor device in this specification refers to all devices that can function by utilizing semiconductor characteristics, and electro-optic devices, semiconductor circuits, and electronic appliances are all semiconductor devices.
2. Description of the Related Art
Attention has been focused on a technique for forming a transistor (also referred to as a thin film transistor (TFT)) with the use of a semiconductor thin film formed over a substrate having an insulating surface. Such a transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) or an image display device (display device). A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor. As another material, an oxide semiconductor material has been attracting attention.
For example, a transistor whose active layer is formed using an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) and having an electron carrier concentration lower than 1018/cm3 is disclosed (see Patent Document 1).